JPH0555629U - Connection impedance correction circuit between logic differential circuits - Google Patents

Abstract

(57) [Abstract] [Purpose] The positive and negative outputs 11 and 12 of the logic differential circuit 1 are connected to the coaxial cables 2A and 2B and the pattern 3A of the printed circuit board 3.
Provided is a connection impedance correction circuit with less reflected waves when transmitting to the positive / negative inputs 4A and 4B of the logical differential circuit 4 by 3B. [Configuration] Connection point 3 between the coaxial cable 2A and the pattern 3A
The correction resistor 6 is connected between C and the connection point 3D of the coaxial cable 2B and the pattern 3B.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 This invention relates to a connection impedance correction circuit for transmitting the positive / negative output of the first logical differential circuit to the positive / negative input of the second logical differential circuit by the pattern of the coaxial cable and the printed circuit board.

[0002]

[Prior Art]

 Next, a conventional impedance correction circuit will be described with reference to FIG. In FIG. 1, 1 and 4 are logical differential circuits, 2A and 2B are coaxial cables, 3 is a printed circuit board, 3A and 3B are patterns of the printed circuit board 3, and 5A and 5B are terminating resistors.

In FIG. 2, the positive output 11 from the logical differential circuit 1 is transmitted by the coaxial cable 2A, and the negative output 12 from the logical differential circuit 1 is transmitted by the coaxial cable 2B. The coaxial cable 2A is connected to the pattern 3A of the printed board 3, and the coaxial cable 2B is connected to the pattern 3B of the printed board 3. The pattern 3A is connected to the positive input 4A of the logical differential circuit 4, and the pattern 3B is connected to the negative input 4B of the logical differential circuit 4. The positive input 4A of the logical differential circuit 4 is terminated by the terminating resistor 5A, and the negative input 4B of the logical differential circuit 4 is terminated by the terminating resistor 5B.

[0004]

[Problems to be solved by the device]

 The patterns 3A and 3B shown in FIG. 2 have a shorter line length than the coaxial cables 2A and 2B, and have large variations in impedance. Patterns 3A and 3B have higher impedance with higher density.

Next, a waveform example of each part of FIG. 2 will be described with reference to FIG. 3A shows the positive output waveform of the logical differential circuit 1, and FIG. 3A shows the positive input waveform of the logical differential circuit 4. Figure 3a shows a waveform with a rise time of 1 ns in the frequency band of 300 to 500 MHz, for example. FIG. 3A shows a state in which reflected waves are generated at the positions P1 and Q1. The reflection coefficient in FIG. 3A is, for example, about 0.17 ρ. The reflected wave in FIG. 3A occurs because the impedance of the transmission path from the logical differential circuit 1 to the logical differential circuit 4 is not matched. FIG. 3C shows the positive input waveform of the logical differential circuit 4 when the impedances of the transmission lines from the logical differential circuit 1 to the logical differential circuit 4 are matched, and the reflected wave of FIG. 3A does not appear.

Impedance matching is required to eliminate reflected waves in the circuit of FIG. In the conventional technique, the impedance of the printed circuit board 3 has a large manufacturing variation and is difficult to control. For this reason, the coaxial cable had to be mounted on the printed circuit board 3. In the conventional impedance correction circuit, it was difficult to secure a space for mounting the correction coaxial cable.

According to the present invention, when the positive and negative outputs of the logic differential circuit 1 are transmitted to the positive and negative inputs 4A and 4B of the logic differential circuit 4 by the coaxial cables 2A and 2B and the patterns 3A and 3B of the printed circuit board 3, the coaxial outputs are transmitted. The purpose is to correct the connection impedance by adding a correction resistor between the connection points between the cables 2A and 2B and the patterns 3A and 3B on the printed circuit board 3 and reduce the reflected waves.

[0008]

[Means for Solving the Problems]

 In order to achieve this object, in the present invention, a correction resistor 6 is connected between a connection point 3C between the coaxial cable 2A and the pattern 3A and a connection point 3D between the coaxial cable 2B and the pattern 3B.

[0009]

[Action]

 Next, the configuration of the impedance correction circuit according to the present invention will be described with reference to FIG. 1C is a connection point between the coaxial cable 2A and the pattern 3A, 3D is a connection point between the coaxial cable 2B and the pattern 3B, 6 is a correction resistor, and the others are the same as those in FIG. That is, in FIG. 1, the correction resistor 6 is connected between the connection points 3C and 3D of FIG.

In FIG. 1, the coaxial cables 2A and 2B have the same impedance, and the patterns 3A and 3B of the printed board 3 have the same impedance. The impedance of the patterns 3A and 3B is higher than the impedance of the coaxial cables 2A and 2B, and is set to be equal to the value of the terminating resistors 5A and 5B. As shown in FIG. 3C, correction is performed by the correction resistor 6 connected between the connection points 3C and 3D so that reflected waves do not occur.

[0011]

【Example】

 For example, when the ECL logic is used and the impedance of the coaxial cables 2A and 2B is 50Ω, the impedance of the patterns 3A and 3B is 70Ω, and the termination resistors 5A and 5B are 70Ω, the resistance value of the correction resistor 6 is about 350Ω.

[0012]

[Effect of the device]

 According to this invention, when the positive / negative output of the first logical differential circuit is transmitted to the positive / negative input of the second logical differential circuit by the pattern of the coaxial cable and the printed circuit board, the connection of the coaxial cable and the printed circuit board pattern is connected. Since a correction resistor is added between the points, the reflected wave of the transmission by the coaxial cable and the printed wiring can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a connection impedance correction circuit according to the present invention.

FIG. 2 is a configuration diagram of an impedance correction circuit according to a conventional technique.

FIG. 3 is a signal waveform diagram of FIG.

[Explanation of symbols]

 1 Logic differential circuit 2A / 2B Coaxial cable 3A / 3B Printed wiring 3C / 3D Connection point 4 Logic differential circuit 4A Positive input 4B Negative input 5A / 5B Termination resistor 6 Correction resistor 11 Positive output 12 Negative output

Claims (1)

[Scope of utility model registration request] 1. The positive output (11) of the first logic differential circuit (1) is provided with a second logic difference between the first coaxial cable (2A) and the first pattern (3A) of the printed circuit board (3). To the positive input (4A) of the drive circuit (4) and the negative output (12) of the first logic differential circuit (1) to the second coaxial cable (2B) and the second output of the printed circuit board (3). Pattern (3
B) transmits to the negative input (4B) of the second logic differential circuit (4) and the positive input (4A) of the second logic differential circuit (4) to the first terminating resistor (5
When connecting A) and connecting the second terminating resistor (5B) to the negative input (4B) of the second logic differential circuit (4), the first coaxial cable (2A) and the first pattern Connect the correction resistor (6) between the first connection point (3C) of (3A) and the second connection point (3D) of the second coaxial cable (2B) and the second pattern (3B). A connection impedance correction circuit between logic differential circuits characterized by the above.